wxGUI: add histogram2 to gui_modules/__init__.py

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@48411 15284696-431f-4ddb-bdfa-cd5b030d7da7

gui/wxpython/gui_modules/__init__.py

@@ -15,6 +15,7 @@ all = [
     "goutput.py",
     "gselect.py",
     "histogram.py",
+    "histogram2.py",
     "layertree.py",
     "location_wizard.py",
     "mapdisp_window.py",